Python - sorting/querying a dictionary?

Question

I'm relatively new to Python (2.7 import future) so please forgive me if this is a stupid question.

I've got a dictionary of values[key]. I'm trying to get the second highest value from the list, but write readable code. I could do it by mapping to sortable types, but it's confusing as hell, and then I would have to juggle the key. Any suggestions for how to do it cleanly would be much appreciated.

the second highest value from what list? Please post your relevant code — dm03514, Apr 28 '14 at 19:16

g.d.d.c · Answer 1 · 2014-04-28T19:29:42.363

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2nd highest value in a dictionary:

from operator import itemgetter
# Note that this now returns a k, v pair, not just the value.
sorted(mydict.items(), key = itemgetter(1))[1]

Or more specifically, the 2nd value in the sorted representation of values. You may need to reverse sort order to get the value you actually want.

edited Apr 28 '14 at 19:29

answered Apr 28 '14 at 19:16

g.d.d.c

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`sorted(mydict.values(), reverse=True)[1]` ? – candu Apr 28 '14 at 19:18
How do I retrieve the key for that value? – cjm2671 Apr 28 '14 at 19:27
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@cjm2671 - I've updated my answer to include retrieving the key as well. While the shorthand is convenient, note from the other question you were linked to that this is `O(N log N)`, while an `O(N)` solution is possible. – g.d.d.c Apr 28 '14 at 19:30

score 0 · Answer 2 · answered Apr 28 '14 at 19:22

If you also want the key associated with that value, I would do something like:

# Initialize dict
In [1]: from random import shuffle
In [2]: keys = list('abcde')
In [3]: shuffle(keys)
In [4]: d = dict(zip(keys, range(1, 6)))
In [5]: d
Out[5]: {'a': 4, 'b': 1, 'c': 5, 'd': 3, 'e': 2}
# Retrieve second highest value with key
In [6]: sorted_pairs = sorted(d.iteritems(), key=lambda p: p[1], reverse=True)
In [7]: sorted_pairs
Out[7]: [('c', 5), ('a', 4), ('d', 3), ('e', 2), ('b', 1)]
In [8]: sorted_pairs[1]
Out[8]: ('a', 4)

The key=lambda p: p[1] tells sorted to sort the (key, value) pairs by the value, and reverse tells sorted to place the largest values first in the resulting list.

score 0 · Answer 3 · answered Apr 28 '14 at 19:23

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This should do the trick:

maximum, max_key = None, None
second, second_key = None, None
for key, value in dictionary.iteritems():
  if maximum < value:
     second = maximum
     second_key = max_key
     maximum = value
     maxi_key = second_key

answered Apr 28 '14 at 19:23

radu.ciorba

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Python - sorting/querying a dictionary?

3 Answers3